Solid polymer dispersions and method for their preparation

ABSTRACT

Solid blends of rubbery polymers and amorphous or crystalline polymers, said blends being free-flowing at temperatures lower than the glass transition temperature or crystalline melting temperature of the amorphous or crystalline polymer, are prepared by intimate mixing procedures. In general, said mixing conditions include high shear conditions sufficient to convert polymer A to dispersed particles coated with polymer B and produce a free-flowing powder blend.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of application Ser.No. 09/696,088, filed Oct. 26, 2000, which in turn is a division ofapplication Ser. No. 09/218,925, filed Dec. 22, 1998, now U.S. Pat. No.6,194,518, which in turn is a continuation-in-part of application Ser.No. 08/959,256, filed Oct. 29, 1997, now abandoned, which in turn is acontinuation-in-part of application Ser. No. 08/742,536, filed Nov. 1,1996, now abandoned, which are incorporated herein by reference.

BACKGROUND OF INVENTION

[0002] This invention relates to polymer dispersions in solid form and amethod for their preparation. More particularly, it relates to thepreparation of polymer blends in solid form.

[0003] The use of elastomeric (i.e., rubbery) polymers as additives inblends comprising other polymers is known. Various rubbery polymers areuseful as impact modifiers, flame retardants and additives conferringother properties on blends in which they are incorporated. While thedispersion of liquid additives in polymeric powders is well known andpreviously documented by Dahms et al. (U.S. Pat. No. 3,301,813), auniform and fine dispersion of rubbery polymers in thermoplastics toform dry free-flowing powders has not been reported.

[0004] U.S. Pat. Nos. 3,824,208, 5,153,238, 5,391,594 and 5,412,014describe the incorporation of fillers such as silica in rubbery polymersto form compositions which exist as free-flowing particles. However, itis sometimes highly desirable to exclude inorganic materials such assilica from polymer blends or coat the surface of the silica particleswith siloxane elastomers, in which case these compositions are no longerfree-flowing . The surface chemistry of the filler in some cases canresult in degradation of the matrix polymer.

[0005] Conventional approaches for obtaining free-flowing powders withelastomeric components include the use of block copolymers, core-shellcopolymers or graft copolymers with thermoplastics. Copolymerization orgrafting of glassy/crystalline thermoplastic prevents agglomeration ofthe rubbery component and enables convenient addition of these impactmodifiers as free-flowing powders in extrusion equipment for meltprocessing. Such approaches however do not provide a cost effectivesolution for preparing free-flowing polymeric dispersions.

[0006] It is difficult, however, to prepare homogeneous blends ofrubbery polymers with other resins, owing to the relativeintractabilities of said rubbery polymers and the slow progress ofdispersion of said polymer in the blend. Examples of some alternativeapproaches for obtaining free-flowing powders include mixing adispersion of an organic thermoplastic polymer with an emulsion of asilicone resin as taught by Fuhr et al. in U.S. Pat. No. 5,100,958. Thismethod is once again not cost effective since it involves a subsequentadjustment of pH for coagulation followed by isolation and drying of thecoagulate. Another method proposed by Vaughn in U.S. Pat. No. 4,153,639involves mixing the resin and the rubbery additive (in this casesilicone gum) in a liquid medium having a component which vaporizesreadily. The liquid medium is contacted with flowing live steam in aconduit and the mixture is fed into a closed chamber from which thesuperheated, vaporized liquid components are removed and a particulateblend is extracted.

[0007] Other practical limitations in melt-melt blending ofthermoplastics with rubbery polymers include the inability to dispersethe rubber phase adequately in the thermoplastic melt using theconventional processing equipment due to excessive shear heating in theextruders and a morphological balance between drop break up (dispersion)and the subsequent coalescence of the dispersed particles.

[0008] Some applications like powder coating require the availability ofthe thermoplastic resin blend in a powdery form. One route for theformation of thermoplastic blend powders involves high temperature meltextrusion of the various melt components followed by grinding of thethermoplastic pellets to obtain a free-flowing powder. The ability todirectly form uniform thermoplastic blends with fine morphologies atlower processing temperatures can provide a direct, cost-effective andsimpler process.

SUMMARY OF INVENTION

[0009] The present invention facilitates the formation of polymer blendsas described herein above. In particular, it makes it possible toprepare blends which are solid and free-flowing, said blends comprisinghigh and often major proportions of rubbery materials such aspolyorganosiloxanes and synthetic elastomers, said blends alsocontaining another resinous constituent. Among the blends that can beproduced are those useful as products in their own right and thoseuseful as master batches suitable for incorporation as additives inother polymer compositions.

[0010] In one of its aspects, the present invention provides a methodfor preparing a blend, said blend comprising: a polyorganosiloxane (A)having at least one of a glass transition temperature (Tg_(a)) or amelting temperature (Tm_(a)), a polyphenylene ether (B) having at leastone of a glass transition temperature (Tg_(b)) or melting temperature(Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A and B are amorphous,Tm_(a)<Tm_(b) when both polymers A and B are crystalline, Tg_(a)<Tm_(b)when polymer A is amorphous and polymer B is crystalline, andTm_(a)<Tg_(b) when polymer A is crystalline and polymer B is amorphous,which comprises intimately mixing said polymers at a suitabletemperature between the lower of Tg_(a) and Tm_(a) and the value ofTg_(b), for a time and under shear conditions sufficient to convertpolymer A to dispersed particles coated with polymer B and produce afree-flowing blend, said blend being free of silica filler and treatedsilica filler. Also provided is a composition prepared by theaforementioned method.

DETAILED DESCRIPTION

[0011] In some embodiments the present invention provides a methodwherein Tg_(a) is below about 160° C., in other embodiments below about50° C., and in still other embodiments below about minus 100° C. In someembodiments the present invention provides a method wherein polymer B iscrystalline. In still other embodiments the present invention provides amethod wherein polymer B is amorphous and Tg_(b) is above about 100° C.It is generally known to those skilled in the art that many, but notall, polymers as commonly obtained comprise a mixture of amorphous andcrystalline fractions. In some particular polymers an amorphous phasepredominates, while in other particular polymers a crystalline phase mayprovide a significant fraction of the total polymer. In other particularembodiments polymer A and polymer B are typically immiscible andincompatible with each other.

[0012] In various embodiments the present invention provides a methodwherein polymer A is a polyorganosiloxane, an ethylene-propylene rubber,polybutadiene, polyisoprene, neoprene, an acrylic rubber, or copolymersthereof, and polymer B is an olefin polymer, a polycarbonate, poly(vinylchloride), a linear polyester, a vinyl aromatic polymer, a polyphenyleneether, a polyimide, a polyethersulfone, a polyetherketone, a polyarylenesulfide, or copolymers thereof. In particular embodiments the presentinvention provides a method wherein polymer B ispoly(2,6-dimethyl-1,4-phenylene ether), poly(butylene terephthalate), orpolyetherimide.

[0013] Provided in yet another embodiment is a method wherein polymers Aand B are mixed in a rotary blade mixer at a blade tip velocity in therange of about 1,000-15,000 cm/sec.

[0014] In another embodiment the instant invention provides acomposition comprising a blend of polymer A having glass transitiontemperature (Tg_(a)) and/or a melting temperature (Tm_(a)), polymer Bhaving glass transition temperature (Tg_(b)) or melting temperature(Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A and B are amorphous,Tm_(a)<Tm_(b) when both polymers A and B are crystalline, Tg_(a)<Tm_(b)when polymer A is amorphous and polymer B is crystalline, andTm_(a)<Tg_(b) when polymer A is crystalline and polymer B is amorphous,said composition being produced by the process of intimately mixing saidpolymers at a suitable temperature between the lower of Tg_(a)and Tm_(a)and the higher of Tg_(b) and Tm_(b), for a time and under shearconditions sufficient to convert polymer A to dispersed particles coatedwith polymer B and produce a free-flowing blend in the form of a powder.In still another embodiment the instant invention provides a compositioncomprising a blend of polymer A having glass transition temperature(Tg_(a)) and/or a melting temperature (Tm_(a)), polymer B having glasstransition temperature (Tg_(b)) or melting temperature (Tm_(b)), whereinTg_(a)<Tg_(b) when polymers A and B are amorphous, Tm_(a)<Tm_(b) whenboth polymers A and B are crystalline, Tg_(a)<Tm_(b) when polymer A isamorphous and polymer B is crystalline, and Tm_(a)<Tg_(b) when polymer Ais crystalline and polymer B is amorphous, said composition beingproduced by the process of intimately mixing said polymers at a suitabletemperature between the lower of Tg_(a) and Tm_(a), and the value ofTg_(b), for a time and under shear conditions sufficient to convertpolymer A to dispersed particles coated with polymer B and produce afree-flowing blend in the form of a powder. In some particularembodiments the free-flowing blend is prepared by the method of theinvention which does not involve melting of polymer B. In otherparticular embodiments polymer B may be plasticized, for example bymixing with at least one other polymer or additive which is at leastpartly miscible with polymer B such that the Tg of the mixture is lowerthan the Tg of polymer B itself, in which case the temperature range forpreparing blends by the present method is at a suitable temperaturebetween the lower of Tg_(a) and Tm_(a), and the value of Tg for themixture of polymer B with at least one other polymer or additive whichis at least partly miscible with polymer B. An example of a plasticizedmixture of a polymer B is a mixture of a polyphenylene ether such aspoly-2,6-dimethyl-1,4-phenylene ether with a polystyrene, which mixturetypically has a Tg in between that of the polyphenylene ether and thepolystyrene dependent upon, among other factors, the relativeproportions of the two polymers in the mixture.

[0015] The free-flowing powders prepared by the method of the presentinvention have a mean particle size in one embodiment in a range ofbetween about 50 microns and about 4000 microns, in another embodimentin a range of between about 100 microns and about 3000 microns, inanother embodiment in a range of between about 200 microns and about2000 microns, in another embodiment in a range of between about 200microns and about 1500 microns, in another embodiment in a range ofbetween about 250 microns and about 1200 microns, in another embodimentin a range of between about 300 microns and about 1000 microns, and instill another embodiment in a range of between about 400 microns andabout 900 microns. In a particular embodiment a free flowing powderblend may be distinguished from a pelletized extrudate made in a meltprocess which pellets typically have at least one dimension greater thanabout 4000 microns.

[0016] In some embodiments the present invention provides a compositionwherein Tg_(a) is below about 160° C., in other embodiments below about50° C., and in still other embodiments below about minus 100° C. In someembodiments the present invention provides a composition wherein polymerB is crystalline. In still other embodiments the present inventionprovides a composition wherein polymer B is amorphous and Tg_(b) isabove about 100° C.

[0017] In various embodiments the present invention provides acomposition wherein polymer A is a polyorganosiloxane, anethylene-propylene rubber, polybutadiene, polyisoprene, neoprene, anacrylic rubber, or copolymers thereof, and polymer B is an olefinpolymer, a polycarbonate, poly(vinyl chloride), a linear polyester, avinyl aromatic polymer, a polyphenylene ether, a polyimide, a.polyethersulfone, a polyetherketone, a polyarylene sulfide, orcopolymers thereof. In particular embodiments the present inventionprovides a composition wherein polymer B ispoly(2,6-dimethyl-1,4-phenylene ether), poly(butylene terephthalate), orpolyetherimide.

[0018] Elastomeric examples of polymer A employed according to thepresent invention are those which have a relatively low glass transitiontemperature Tg_(a). The value of Tg_(a) is generally below about 25° C.and may be below 0° C. For example, polydiorganosiloxane gums useful inthe invention may have Tg values down to about minus 127° C. with amelting point of about minus 40° C. Polymer A typically has a highviscosity, most often in the range of about 500,000 to about 20,000,000centipoise at a shear rate on the order of 10 sec-⁻¹, however polymershaving viscosities as low as 5,000 and above about 20,000,000 may alsobe used. In some embodiments examples of polymer A have a number averagemolecular weight of greater than about 10,000 and in other embodimentsgreater than about 20,000.

[0019] In various embodiments polymer A comprises at least onepolyorganosiloxane, especially polydialkylsiloxanes such aspolydimethylsiloxane and their fluorinated derivatives such aspoly(trifluoropropylmethylsiloxane). However, other rubbery polymersincluding ethylene-propylene rubbers, polybutadiene, polyisoprene,neoprene (polychloroprene) and acrylic rubbers, such as poly(ethylacrylate), poly(isobutyl acrylate) and poly(n-butyl acrylate) orcopolymers thereof may also be employed.

[0020] Polymers useful as polymer B may be amorphous or crystalline.When amorphous, they are characterized by their Tg_(b) value; whencrystalline, the crystalline melting temperature (Tm_(b)) may be moresignificant. Thus, there is a temperature span which is above the glasstransition temperature (Tg_(a)) or melting point (Tm_(a)) of polymer Aand below the higher of the glass transition temperature (Tg_(b)) orcrystalline melting temperature (Tm_(b)) of polymer B.

[0021] Illustrative polymers useful as polymer B include olefin polymerssuch as polyethylene and polypropylene, polycarbonates, poly(vinylchloride), linear polyesters such as poly(ethylene terephthalate) andpoly(butylene terephthalate), vinylaromatic polymers includingpolystyrene and styrene-acrylonitrile copolymers, polyphenylene ethers,polyimides (including polyetherimides), polyethersulfones,polyetherketones and polyarylene sulfides. In some embodiments polymersuseful as polymer B are those having glass transition temperatures aboveabout 150° C. In particular embodiments polymers useful as polymer Bcomprise polyphenylene ethers, such as, but not limited to,poly(2,6-dimethyl-1,4-phenylene ether) andpoly(2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene ether).

[0022] The compositions of the invention may include additives such asfillers, plasticizers, compatibilizers, lubricants, UV screeners, flameretardants, antistatic agents, antioxidants, and the like. In particularembodiments compositions exclude inorganic fillers such as silica fillerand treated silica filler.

[0023] In a particular embodiment of the invention, polymers A and B aremixed under high shear conditions, at a temperature higher than Tg_(a)or Tm_(a) and lower than the higher of Tg_(b) and Tm_(b). In anotherparticular embodiment of the invention, polymers A and B are mixed underhigh shear conditions, at a temperature higher than Tg_(a) or Tm_(a) andlower than the value of Tg_(b). Mixing is generally conducted in one ormore discrete steps rather than continuously as in an extruder, andunder high shear conditions sufficient to produce a composition of thetype described hereinafter. High shear mixers of this type are known inthe art and include Waring blenders, Henschel mixers, Drais mixers andmixer-granulators of the type manufactured by Littleford Bros.,Florence, Ky.

[0024] In general, both polymers are charged in their entirety beforemixing begins. It is within the scope of the invention, however, to addpolymer A and polymer B incrementally, so as to maintain conditionsunder which a dispersion of polymer A in solid polymer B is formed.

[0025] It has been shown that initially, a dispersion of gum (polymer A)in solid (polymer B) is formed. During the high shear mixing process, aprogressive breakdown of the particle size of polymer A occurs.Simultaneously, the particles of polymer B coat those of polymer A toform a solid, particulate blend which is a solid dispersion of polymer Ain polymer B and which is free-flowing at temperatures below the higherof Tg_(b) and Tm_(b).

[0026] The proportions of polymers A and B, as well as the mixing timeand conditions, are chosen to ensure that all particles of polymer A aredispersed and coated. If the mixing time is too long, polymer A willform particles so small that the quantity of polymer B will beinadequate to fully coat them, whereupon reagglomeration will take placeimmediately or upon storage.

[0027] Thus, suitable proportions and mixing conditions can bedetermined by simple experimentation. Weight ratios of polymer B topolymer A are in various embodiments in the range of about 1:1 to about5:1. In the case of a rotary blade mixer, blade tip velocities in therange of about 1,500 to about 15,000 cm/sec are generally adequate toproduce the required high shear mixing.

[0028] The blending temperature is not particularly critical. In oneembodiment the blending temperature is between the lower of Tg_(a) andTm_(a) and the higher of Tg_(b) and Tm_(b). In another embodiment theblending temperature is between the lower of Tg_(a) and Tm_(a) and thevalue of Tg_(b). In a particular embodiment where Tg_(a) is below aboutand Tg_(b) or Tm_(b) is above about 150° C., blending at moderatetemperatures in the range of about 20° C. to about 75° C., andespecially at ambient temperature of about 25° C., is satisfactory. Inother embodiments, polyethylene with a Tm of about 10° C. may beemployed as polymer A with a polyphenylene ether having a Tg of 210° C.as polymer B, if blending is at a temperature typically around 150° C.In various embodiments the blending temperature is below both Tg_(b) andTm_(b).

[0029] Following the blending operation of the present invention, it issometimes desirable to extrude and to pelletize the polymer blend of theinvention to form a storable material. Depending on the constituentsemployed, this storable material may itself be a useful polymercomposition or may be a master batch or an additive for incorporationinto other polymer compositions.

[0030] Without further elaboration, it is believed that one skilled inthe art can, using the description herein, utilize the present inventionto its fullest extent. The following examples are included to provideadditional guidance to those skilled in the art in practicing theclaimed invention. The examples provided are merely representative ofthe work that contributes to the teaching of the present application.Accordingly, these examples are not intended to limit the invention, asdefined in the appended claims, in any manner. All parts are by weight.

EXAMPLE 1

[0031] A mixture of 25 parts of a vinyl-terminated polydimethylsiloxanegum (Tg about minus 127° C. & Tm about minus 40° C.) having a viscosityof about 3.9 million centipoise at a shear rate of about 10.14 sec-⁻¹and 100 parts of a poly(2,6-dimethyl-1,4-phenylene ether) having aTg_(b) of about 210° C. having an intrinsic viscosity of 0.4 dl/g (inchloroform at 25° C.) was mixed at room temperature (about 25° C.) in a

[0032] Waring blender at high speed for 10 minutes. The desired blendwas obtained as a free-flowing powder, with 2.36 parts of unblendedsilicone remaining. The blend was capable of being molded, as shown by acompression molding operation at 300° C. Mixing time and shear rate arecritical for controlling the amount of unblended silicone.

EXAMPLE 2

[0033] The procedure of Example 1 was repeated, except that mixing wasconducted in a Henschel mixer at a tip speed of 4,000 cm/s and ambienttemperature. The product was a free-flowing powder capable of extrusionand molding with no detectable unblended silicone.

EXAMPLE 3

[0034] The procedure of Example 2 was employed to prepare a free-flowingpowder of 4 parts of polyethylene powder (Tm_(b) about 120° C., andTg_(b) about minus 80° C.) and part of methyl-stoppedpolydimethylsiloxane gum (Tg about minus 127° C. & Tm about minus 40°C.) having a viscosity of about 3,900,000 centipoise at 10.14 sec-⁻¹.The blend was capable of extrusion and molding.

EXAMPLE 4

[0035] The procedure of Example 3 was repeated, substituting 4 parts ofpolystyrene powder (Tg_(b) about 100° C.) for the polyethylene powder. Asimilar product was obtained.

EXAMPLE 5

[0036] The procedure of Example 4 was repeated, substituting 4 parts ofbisphenol A polycarbonate powder (Tg_(b) about 162° C.) for thepolyethylene powder. A similar product was obtained.

EXAMPLE 6

[0037] The procedure of Example 1 was repeated, using a blend of 1 parteach of the polyphenylene ether (Tg_(b) about 210° C.) and anethylene-propylene rubber (Tg_(a) about minus 80° C.). A well dispersed,free-flowing powder with a shelf life of at least one month wasobtained. The blend was capable of extrusion and molding.

[0038] While the invention has been illustrated and described in typicalembodiments, it is not intended to be limited to the details shown,since various modifications and substitutions can be made withoutdeparting in any way from the spirit of the present invention. As such,further modifications and equivalents of the invention herein disclosedmay occur to persons skilled in the art using no more than routineexperimentation, and all such modifications and equivalents are believedto be within the spirit and scope of the invention as defined by thefollowing claims. All U.S. Patents and U.S. Patent applications citedherein are incorporated herein by reference.

What is claimed is:
 1. A method for preparing a blend, said blendcomprising: a polyorganosiloxane (A) having at least one of a glasstransition temperature (Tg_(a)) or a melting temperature (Tm_(a)), apolyphenylene ether (B) having at least one of a glass transitiontemperature (Tg_(b)) or melting temperature (Tm_(b)), whereinTg_(a)<Tg_(b) when polymers A and B are amorphous, Tm_(a)<Tm_(b) whenboth polymers A and B are crystalline, Tg_(a)<Tm_(b) when polymer A isamorphous and polymer B is crystalline, and Tm_(a)<Tg_(b) when polymer Ais crystalline and polymer B is amorphous, which comprises intimatelymixing said polymers at a suitable temperature between the lower ofTg_(a) and Tm_(a) and the value of Tg_(b), for a time and under shearconditions sufficient to convert polymer A to dispersed particles coatedwith polymer B and produce a free-flowing blend, said blend being freeof silica filler and treated silica filler.
 2. The method according toclaim 1 wherein Tg_(a) is below about 160° C.
 3. The method according toclaim 2 wherein Tg_(a) is below about 50° C.
 4. The method according toclaim 3 wherein Tg_(a) is below about minus 100° C.
 5. The methodaccording to claim 2 wherein polymer B is crystalline.
 6. The methodaccording to claim 3 wherein polymer B is amorphous and Tg_(b) is aboveabout 100° C.
 7. The method according to claim 1 wherein thepolyorganosiloxane comprises a polydimethylsiloxane.
 8. The methodaccording to claim 1 wherein the polyphenylene ether (B) comprises apoly(2,6-dimethyl-1,4-phenylene ether).
 9. The method according to claim1 wherein said polymers are mixed in a rotary blade mixer at a blade tipvelocity in the range of about 1,000 to about 15,000 cm/sec.
 10. Themethod of claim 1 wherein the polyorganosiloxane has a viscosity in arange between 5,000 and about 20,000,000 centipoise at a shear rate ofabout 10 sec⁻¹.
 11. A method for preparing a blend, said blendconsisting essentially of: a polyorganosiloxane (A) having at least oneof a glass transition temperature (Tg_(a)) or a melting temperature(Tm_(a)), a poly-2,6-dimethyl-1,4-phenylene ether (B) having at leastone of a glass transition temperature (Tg_(b)) or melting temperature(Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A and B are amorphous,Tm_(a)<Tm_(b) when both polymers A and B are crystalline, Tg_(a)<Tm_(b)when polymer A is amorphous and polymer B is crystalline, andTm_(a)<Tg_(b) when polymer A is crystalline and polymer B is amorphous,which comprises intimately mixing said polymers at a suitabletemperature between the lower of Tg_(a) and Tm_(a) and the value ofTg_(b), for a time and under shear conditions sufficient to convertpolymer A to dispersed particles coated with polymer B and produce afree-flowing blend, said blend being free of silica filler and treatedsilica filler.
 12. A composition comprising a blend of: apolyorganosiloxane (A) having at least one of a glass transitiontemperature (Tg_(a)) or a melting temperature (Tm_(a)), a polyphenyleneether (B) having at least one of a glass transition temperature (Tg_(b))or melting temperature (Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers Aand B are amorphous, Tm_(a)<Tm_(b) when both polymers A and B arecrystalline, Tg_(a)<Tm_(b) when polymer A is amorphous and polymer B iscrystalline, and Tm_(a)<Tg_(b) when polymer A is crystalline and polymerB is amorphous, produced by the process of intimately mixing saidpolymers at a suitable temperature between the lower of Tg_(a) andTm_(a) and the value of Tg_(b), for a time and under shear conditionssufficient to convert polymer A to dispersed particles coated withpolymer B and produce a free-flowing blend, said composition being freeof silica filler and treated silica filler.
 13. The compositionaccording to claim 12 wherein Tg_(a) is below about 160° C.
 14. Thecomposition according to claim 13 wherein Tg_(a) is below about 50° C.15. The composition according to claim 14 wherein the Tg_(a) is belowabout minus 100° C.
 16. The composition according to claim 12 whereinpolymer B is crystalline.
 17. The composition according to claim 14wherein polymer B is amorphous and Tg_(b) is above about 100° C.
 18. Thecomposition according to claim 12 wherein the polyorganosiloxanecomprises a polydimethylsiloxane.
 19. The composition according to claim12 wherein the polyphenylene ether (B) comprises apoly(2,6-dimethyl-1,4-phenylene ether).
 20. The composition of claim 12wherein said polymers are mixed in a rotary blade mixer at a blade tipvelocity in the range of about 1,000 to about 15,000 cm/sec.
 21. Thecomposition of claim 12 wherein the polyorganosiloxane has a viscosityin a range between 5,000 and about 20,000,000 centipoise at a shear rateof about 10 sec⁻¹.
 22. A composition consisting essentially of a blendof: a polyorganosiloxane (A) having at least one of a glass transitiontemperature (Tg_(a)) or a melting temperature (Tm_(a)), apoly-2,6-dimethyl-1,4-phenylene ether (B) having at least one of a glasstransition temperature glass transition temperature (Tg_(b)) or amelting temperature (Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A andB are amorphous, Tm_(a)<Tm_(b) when both polymers A and B arecrystalline, Tg_(a)<Tm_(b) when polymer A is amorphous and polymer B iscrystalline, and Tm_(a)<Tg_(b) when polymer A is crystalline and polymerB is amorphous, produced by the process of intimately mixing saidpolymers at a suitable -temperature between the lower of Tg_(a) andTm_(a)and the value of Tg_(b), for a time and under shear conditionssufficient to convert polymer A to dispersed particles coated withpolymer B and produce a free-flowing powder blend, said compositionbeing free of silica filler and treated silica filler.